I've seen this a couple of times, but this time I captured a sample. TM2 was running in the background when I noticed it was using the CPU a lot. I had a couple of documents and projects open some of which are in a Mercurial repository. From the sample it looks like TM2 is scanning directories for some reason.
Version 2.0 (9090) OS X 10.7.3
Thanks, /Staffan